Bird Community Structure Along a Trekking Corridor of Sikkim Himalaya: a Conservation Perspective
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Biological Conservation 102 (2001) 1–16 www.elsevier.com/locate/biocon Bird community structure along a trekking corridor of Sikkim Himalaya: a conservation perspective N. Chettria, E. Sharmaa,*, D.C. Debb aG. B. Pant Institute of Himalayan Environment and Development, Sikkim Unit, PO Tadong, Sikkim, 737102 India bDepartment of Zoology, North Bengal University, Raja Rammohanpur, Darjeeling, India Received 20 April 2000; received in revised form 10 February 2001; accepted 9 March 2001 Abstract Bird community structure was studied in the Yuksam–Dzongri trekking corridor of the Sikkim Himalaya, India. Nineteen transects with a total of 266 samplings were made in the forests along the corridor during June 1997 to June 1999. Human utilised forest (open canopy forest) and relatively unutilised forest (closed canopy forest) were designated for the study at two ecological zones, i.e. lower forest (1780–2350 m a.s.l.) and upper forest (2350–3600 m) depending on the natural resources utilisation pattern by local community living in the area and for tourism purposes. There were visible changes in the open and closed canopy forests in diameters at breast height class distribution of trees leading to distinct variation in the habitat types. Among the 143 species of birds observed during the study, a handful of species were found as habitat specific and about 40% were common to all the four habitat types. Both bird species richness and diversity were higher at the open canopy conditions compared with closed canopy, but the differences were not statistically significant. On the other hand, both the indices showed strong and significant negative relationship with the elevation. These diversity indices were also significantly higher during the summer compared with the winter season. The open canopy conditions exhibited comparatively more species of birds that were perturbated by human settlements than those species found at the closed canopy (mostly forest interior) and vice versa. Though the study could not trace out the effect of patch size brought about by human caused disturbances, the Yuksam–Dzongri trekking corridor possesses diverse habitat types as well as bird species resulted from heterogeneous habitat conditions. It is therefore important to emphasise disturbance study for threshold level assessment so that generalists as well as forest interior species could be managed through conservation efforts. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Forest types; Species richness and diversity; Habitat conditions; Seasonality 1. Introduction Javed, 1996; Safiq et al., 1997). Large scale habitat changes are occurring globally for fulfilling human Bird community evaluation has become an important needs that have caused habitat destruction, fragmenta- tool in biodiversity conservation and for identifying tion and degradation, necessiting assessment on the conservation actions in areas of high human pressure impacts of such change on birds (Brash, 1987; Whitten (Kremen, 1992; Safiq et al., 1997). Indian subcontinent et al., 1987; Khan et al., 1993). Determinations of bird is known for diverse and rich bird species whose tax- population in different habitats are central to under- onomy, distribution and their general habitat char- standing the community structure and niche relation- acteristics are well documented in India (Jerdon, 1862– ships, as well as for intelligent management of 1964; Bates and Lowther, 1952; Ali and Ripley, 1983). populations. Moreover seasonal monitoring is equally However, only a very little is known about bird com- important to trace the dynamic movement of birds in munity structure and their dynamics in India (Daniels, such habitats (Green and Catterall, 1998). 1989; Khan et al., 1993; Johnsingh and Joshua, 1994; The Eastern Himalaya (Khangchendzonga region) supports a wide diversity of birds resulting from complex physiography and bioclimatic zonation (Ives and Mes- * Corresponding author. Tel./fax: +91-3592-31090. serli, 1989) and also because of their location at the con- E-mail address: [email protected] (E. Sharma). vergence of the Palaearctic and Oriental Zoogeographical 0006-3207/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(01)00092-1 2 N. Chettri et al. / Biological Conservation 102 (2001) 1–16 Realms (Inskipp, 1989). The area has been identified by issues of common interest for management (Sharma, the Birdlife International as a Priority I Endemic Bird 1997). Yuksam–Dzongri trekking corridor (26 km long) Area since it supports 25 restricted range bird species, of encompasses elevation from 1780 to 4000 m (Fig. 1). which 21 are confined to the region (Bibby, 1992). The trail passes through Sachen, Bakhim and Tshoka in Among eight species which were considered to be at risk the south-western part of Khangchendzonga Biosphere and listed as rare, vulnerable or endangered in the Reserve in Sikkim, India. Yuksam is a trailhead for this region (Carpenter, 1996), four species (satyra tragopan, corridor and leads to the Base Camp, Dzongri, Nepal cutia, short billed minivet and little pied fly- Thangsing and Gocha La in the West Sikkim (Fig. 1). catcher) have been recorded in the present study area Yuksam (1780 m) has 11 settlements with 274 house- (Chettri, 2000). holds comprising of 1573 people. One settlement with Bird studies in Sikkim date back to the 19th century eight households is inside the biosphere reserve at and many accounts on birds of Sikkim are available Tshoka (3000 m) on the trail. The majority of the ethnic (Bulger, 1869; Blandford, 1872; Gammie, 1877; Brooks, people of Yuksam are Subbas, followed by Bhutias, 1880; Ludlow and Kinnear, 1937, 1944; Mills, 1944; Lepchas, Nepalis and Tibetan Refugees mostly at Maclaren, 1947, 1948; Sen, 1948, 1957). Ali’s (1989) Tshoka. The primary occupation of the people is farm- ornithological work in the region is the most exhaustive ing while some are associated with tourism in the form to date. However, only a few more recent survey reports of lodge operators, porters, yakmen, cooks and guides are available. Some recent works have added about for trekking. Firewood and fodder collection, interior 30+ species to the list (Ganguli-Lachungpa, 1998). forest grazing and leaf litter collection are common Although bird taxonomy, distribution and their general practices among the different ethnic groups. Tourism is habitats have been documented, there have been no increasing in the area at a rapid rate (Rai and Sundriyal, attempts for bird community study in Sikkim. 1997) and more people are engaged in this profession. Yuksam–Dzongri trekking corridor in west Sikkim is Annually, about 2000 domestic and foreign tourists visit an important tourist destination with great potential for the area. More than 150 support staff, 140 dzos (cross of bird watching. Disturbances such as firewood extrac- cow and yak) and 12 horses (pack animals) operate in tion, fodder lopping and cattle grazing are worldwide this trekking trail on an average of six times a year. The problem and have increased during the last two decades Himalayan Mountaineering Institute (HMI) conducts in this trekking corridor due to growth in tourism and training for about 500 trainees annually in the area. population. These have resulted in the fragmentation Trekking tour staff including porters hired by travel and deterioration of wildlife habitats and also affecting agents and HMI trainees collect firewood for cooking the natural beauty of the area. Vegetation structure and heating purposes all along the corridor. This has showed remarkable changes in species composition at been one of the major factors of the forest destruction. human disturbed locations compared with relatively Four sampling stands were selected along the Yuksam– undisturbed areas along the corridor (Chettri, 2000). Dzongri trekking corridor (Fig. 1). Dominant trees and This could have major negative impacts on wildlife. An selective important species of all stand types are presented exploratory monitoring of birds in the area that in Table 1. Out of these four stands, two were located at encompassed a wide range of altitude and diverse forest warm temperate broadleaf forest having an elevation types is of special importance because of disturbances range 1780–2350 m and we designated the area as lower along the trek in recent years. This work would be use- forest (LF). Settlements around Yuksam generally ful for comparison in the follow-up study after a few depend on this forest for firewood, fodder and timber. more years of tourism in the area. The paper is an The other two stands were located at cool-temperate attempt to assess (1) bird diversity, (2) species composi- and sub-alpine zone having an elevation range 2350– tion and abundance and (3) seasonal variation on bird 3600 m, were designated as upper forest (UF). Settle- community structure at highly disturbed and relatively ment from Tshoka and tourism depend on this forest. undisturbed forests along the Yuksam–Dzongri trek- king corridor of west Sikkim. The study provides infor- 2.1. Vegetation surveys mation on effects on bird community in relation to habitat management implications. A total of 19 permanent plots measuring 30Â40 m were laid along the trekking corridor. The plots rela- tively undisturbed and distant from the settlement with 2. Methods >40% canopy cover, were designated as closed canopy forest (CC), while the plots extensively disturbed located The Khangchendzonga area is a unique mountain near the human settlement with <40%